Field of the Invention
The present invention relates to mobile communication.
Related Art
3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) that is an advancement of UMTS (Universal Mobile Telecommunication System) is being introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonal frequency division multiple access) is used for downlink, and SC-FDMA (single carrier-frequency division multiple access) is used for uplink.
Such LTE may be divided into a frequency division duplex (FDD) type and a time division duplex (TDD) type.
As set forth in 3GPP TS 36.211 V10.4.0, the physical channels in 3GPP LTE may be classified into data channels such as PDSCH (physical downlink shared channel) and PUSCH (physical uplink shared channel) and control channels such as PDCCH (physical downlink control channel), PCFICH (physical control format indicator channel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH (physical uplink control channel).
Meanwhile, as the spread of smart phones, users require faster data communications. As such, at the moment when high-speed data communications are required, it may be inefficient for a mobile carrier to provide an FDD-based service only or a TDD-based service only conventionally in the aspect of frequency use. As a result, it may be desirable to have a UE to access both to a cell that uses FDD and to a cell that uses TDD at the same time. In order to realize this, there is talk to combine an FDD-based cell and a TDD-based cell in carrier aggregation (CA) technology in the next generation mobile communication system.
However, in case that the FDD-based cell and the TDD-based cell are included in the carrier aggregation (CA) as above, the HARQ operation of a UE becomes problematic.